Since the callback function called by blk_mq_queue_tag_busy_iter() may sleep calling synchronize_rcu() from __blk_mq_update_nr_hw_queues() is not sufficient to wait until blk_mq_queue_tag_busy_iter() has finished. Instead of making __blk_mq_update_nr_hw_queues() wait until q->q_usage_counter == 0 is globally visible, do not iterate over tags if the request queue is frozen.
Cc: Christoph Hellwig <[email protected]> Cc: Hannes Reinecke <[email protected]> Cc: James Smart <[email protected]> Cc: Ming Lei <[email protected]> Cc: Jianchao Wang <[email protected]> Cc: Keith Busch <[email protected]> Cc: Dongli Zhang <[email protected]> Cc: <[email protected]> Fixes: 530ca2c9bd69 ("blk-mq: Allow blocking queue tag iter callbacks") # v4.19. Signed-off-by: Bart Van Assche <[email protected]> --- block/blk-mq-tag.c | 10 +++++----- block/blk-mq.c | 5 +---- 2 files changed, 6 insertions(+), 9 deletions(-) diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c index a4931fc7be8a..89f479634b4d 100644 --- a/block/blk-mq-tag.c +++ b/block/blk-mq-tag.c @@ -383,14 +383,13 @@ void blk_mq_queue_tag_busy_iter(struct request_queue *q, busy_iter_fn *fn, /* * __blk_mq_update_nr_hw_queues() updates nr_hw_queues and queue_hw_ctx - * while the queue is frozen. So we can use q_usage_counter to avoid - * racing with it. __blk_mq_update_nr_hw_queues() uses - * synchronize_rcu() to ensure this function left the critical section - * below. + * while the queue is frozen. Hold q_usage_counter to serialize + * __blk_mq_update_nr_hw_queues() against this function. */ if (!percpu_ref_tryget(&q->q_usage_counter)) return; - + if (atomic_read(&q->mq_freeze_depth)) + goto out; queue_for_each_hw_ctx(q, hctx, i) { struct blk_mq_tags *tags = hctx->tags; @@ -405,6 +404,7 @@ void blk_mq_queue_tag_busy_iter(struct request_queue *q, busy_iter_fn *fn, bt_for_each(hctx, &tags->breserved_tags, fn, priv, true); bt_for_each(hctx, &tags->bitmap_tags, fn, priv, false); } +out: blk_queue_exit(q); } diff --git a/block/blk-mq.c b/block/blk-mq.c index 652d0c6d5945..f9fc1536408d 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -3226,10 +3226,7 @@ static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set, list_for_each_entry(q, &set->tag_list, tag_set_list) blk_mq_freeze_queue(q); - /* - * Sync with blk_mq_queue_tag_busy_iter. - */ - synchronize_rcu(); + /* * Switch IO scheduler to 'none', cleaning up the data associated * with the previous scheduler. We will switch back once we are done -- 2.21.0.196.g041f5ea1cf98
